Claims that Washington spied on Japanese trade officials, among others, came just as delegates negotiating a vast free-trade agreement known as the Trans-Pacific Partnership failed to reach a final deal after several days of intense talks in Hawaii.

The US and Japan are the two biggest economies in the 12-nation negotiations, but they have sparred over key issues including auto sector access and opening up Japan's protected agricultural markets.

'Intimate knowledge'

WikiLeaks said the US intercepts showed "intimate knowledge of internal Japanese deliberations" on trade issues, nuclear policy, and Japan's diplomatic relations with the US.

"The reports demonstrate the depth of US surveillance of the Japanese government, indicating that intelligence was gathered and processed from numerous Japanese government ministries and offices," it said.

Shinzo Abe, Japan's prime minister, did not appear to be a direct target of phone tapping but senior politicians were.

Yoichi Miyazawa, Japan's trade minister; Haruhiko Kuroda, Bank of Japan governor; and officials of Mitsubishi company were in the sights of US intelligence, WikiLeaks said.

The leaks come as Abe seeks to expand the role of Japan's military, a move applauded by the US but deeply unpopular at home.

"This will be a great embarassment for the US, but it is not going to derail the relationship," Al Jazeera's Harry Fawcett, reporting from the Japanese city of Hiroshima, said.